Systems for conversion of water into hydrogen and sorption of hydrogen in electronic devices

ABSTRACT

The invention teaches a system suitable for use in a water-sensitive electronic device which comprises two superimposed layers, the first material of which is formed of a material capable of sorbing hydrogen, the second material formed of a material capable of converting water into hydrogen; a screen of the type with light-emitting organic diodes comprising the system according to the invention.

REFERENCE TO PRIORITY DOCUMENTS

[0001] This application claims priority under 35 U.S.C. 119 to ItalianApplication MI2001A2010, filed on Sep. 27, 2001, which is incorporatedby reference for all purposes.

BACKGROUND

[0002] It is generally known in the art that the functionality of manyelectronic devices can be altered by the contact with water, even ifonly present in traces. In semiconductor devices water can oxidize theelectric contacts or chemically alter some parts thereof, or of laseramplifiers used in optical fiber communications. This is described inEP-A-720260.

[0003] An electronic application of high industrial interest whereinabsence of water is requested are electroluminescent screens based onthe use of organic materials, is known in the field as OLEDs (from“Organic Light Emitting Devices”).

[0004] The structure of an OLED is formed of a first transparent,essentially planar support, generally made of glass or of a plasticpolymer; a first series of transparent linear and mutually parallelelectrodes (generally having anode functionality), deposited on thefirst support; a double layer of different electroluminescent organicmaterials, of which the first layer is a conductor of electronicvacancies (also defined “holes”) and the second of electrons, depositedon the first set of electrodes; a second series of linear and mutuallyparallel electrodes (generally having cathode functionality) that areorthogonally oriented with respect to those of the first series, incontact with the upper side of the double layer of organic materials, sothat the latter is comprised between both series of electrodes; and asecond not necessarily transparent support that may be made of glass,metal or plastics and is substantially planar and parallel to the firstsupport. The two supports are secured to each other along theirperimeter, generally by glueing, so that the active part of thestructure (electrodes and electroluminescent organic materials) is in aclosed space. The first transparent support is the part where the imageis visualized, whereas the second support generally has only thefunction of closing and backing the device, in order to confermechanical resistance thereto.

[0005] The anode is formed of a transparent conductive material,generally a mixed oxide of indium and tin (In₂O₃—SnO₂) which has thefeatures of a semiconductor, known in the field with the acronym ITO(from “Indium Tin Oxide”), whereas the cathode is formed of alkali-earthmetals, such as Ba, Ca, and Mg—Ag and Al—Li alloys. When a potentialdifference is applied to the electrodes, the electrons and the holes areconveyed to the organic material double layer and combine leading to theformation of photons, whose wave length depends on the nature of theorganic material used.

[0006] For a description of the operating principles of OLEDs andgreater details on their structure one can refer to the abundantliterature of the field.

[0007] A problem encountered with the functioning of OLEDs is theirdeterioration following to exposure to moisture, which can react withthe organic materials (generally polyunsaturated and therefore ratherreactive species), as well as with the cathode, formed of particularlyreactive metals. The portions concerned with these reactions loose theirlight-emitting functionality, thus forming black spots on the screensurface.

[0008] In order to overcome this problem, international publication WO99/03122 describes the introduction into the internal space of an OLEDof a gas reactive towards water, selected for example among silanes,trimethylaluminum or triethylaluminum. These gases react quickly withthe water molecules subtracting them from the internal space of the OLEDand generating reaction products which are not detrimental for thefunctioning of the device. The introduction of a gas in an OLED duringthe production thereof is however difficult to realize.

[0009] U.S. Pat. No. 5,882,761 teaches that the use of solid materialswhich chemically fix water by remaining in the solid state, such as forexample calcium oxide (CaO). A possible problem with the use of thiskind of sorbers is that these materials are generally in powder form,and therefore must be retained by a sheet (for example a nonwovenfabric) permeable to water but able to retain the powder particles. Dueto the use of the powder material and of the permeable sheet, theminimum thickness of the component intended for water sorption cannot belower than limit values of about 0.3-0.4 mm, whereas OLEDsmanufacturers, in order to fully exploit the potentialities of theseflat and thin screens, require moisture sorbing systems which have lowerthickness values than the above mentioned ones. Another problem thatdoes not allow the decrease the tickness of the sorbing systems based onthe use of CaO or similar is the reduction of the water sorbingcapacity.

[0010] International publication WO 98/59356 teaches the use of a gettermaterial arranged inside the OLED and fixed onto the second support.This document indicates some alternatives to calcium oxide for watersorption; in particular it indicates the possibility to use materialssuch as barium, lithium, calcium, barium oxide or similar.

[0011] In particular, the metals lithium, barium, and calcium, beingparticularly reactive towards water, can be used in the devices inlimited quantities.

[0012] Said metals react with water according to the reaction:

2M+2H₂O→2M(OH)+H₂ (wherein M: lithium)

M+2H₂O→M(OH)₂+H₂ (wherein M: barium and calcium)

[0013] As it can be noted from the reaction stoichiometry, one or twomolecules of metal hydroxides and one molecule of hydrogen are formedevery two reacted water molecules. These metals are very reactive, and adrawback is that hydrogen can collect in the OLED thus building up apartial pressure inside the device which can pose safety problems.

[0014] Although hydrogen diffuses through the glue used for fixing thetwo supports of the device and therefore can move outwards, the velocityof hydrogen formation can be higher than the hydrogen permeationvelocity through the OLED sealing, thus causing a continuous increase ofthe gas quantity in the internal space of the device.

BRIEF DESCRIPTION OF THE INVENTION

[0015] The present invention relates to systems for the conversion ofwater into hydrogen and for hydrogen sorption in electronic devices andto a process for manufacturing such systems. The invention thereforeprovides a system for the combined removal of water and hydrogen, to beused in water sensible devices, in a preferred use, for screenscontaining electroluminescent organic materials. In one embodiment, thesystem includes two superimposed layers directly in contact with eachother, one of which is formed of a material capable of sorbing hydrogen,the other formed of a material capable of converting water intohydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] These advantages and the features of the invention will appear tothose skilled in the art from the following detailed description withreference to the accompanying drawings, wherein:

[0017]FIG. 1 schematically shows in cross-section an OLED device withouta gas sorbing system;

[0018]FIG. 2 shows a support of an OLED device, whereon the systemaccording to a first embodiment of the invention;

[0019]FIG. 3 shows a support of an OLED device, whereon the systemaccording to the invention has been formed, in a alternate embodiment ofthe invention;

[0020]FIG. 4 shows a support of an OLED device, whereon the systemaccording to the invention has been formed, in a second alternateembodiment of the invention;

[0021]FIG. 5 schematically shows a possible manufacturing process of thefirst embodiment;

[0022]FIG. 6 schematically shows a manufacturing process of the secondembodiment;

[0023]FIG. 7 schematically shows a first possible manufacturing processof the third embodiment;

[0024]FIG. 8 schematically shows a second possible manufacturing processof the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0025] As previously stated, the invention includes function of removingtraces of water and hydrogen from the internal space of electronicdevices. To this end, it includes a layer of material capable ofconverting water into hydrogen and a layer of hydrogen sorbing materialwhich is deposited on a substrate.

[0026] Various hydrogen sorbing materials can be used in differentembodiments of the invention and include: titanium, zirconium,titanium-zirconium alloys, alloys of titanium containing a weightpercentage of titanium not lower than 50%, zirconium alloys containing aweight percentage of zirconium not lower than 50%. Also, someunsaturated organic compounds coupled with traditional hydrogenationcatalysts can be used, which is described by international publicationWO 99/48125, which is incorporated by reference. The use of unsaturatedorganic molecules of low molecular weight provides significantadvantage, such as for example 1,4-bis(phenylethynylbenzene), coupledfor example with metallic palladium, since they can be easily depositedin thin layers on substrates through evaporation.

[0027] The material for converting water into hydrogen is selected inthe group of the alkali or alkali-earth metals; although many materialscan be used barium is used in a preferred embodiment.

[0028] In the case of an OLED the layer facing the internal space can beformed both of a hydrogen sorbing material and of a material capable ofconverting water into hydrogen; preferably, it is formed of the latter,so that in the following reference will be made to such a configuration.Furthermore, the two layers are superimposed and in contact with eachother and can have the same or different shape and size; preferably theexternal layer covers entirely the internal one.

[0029] The substrates on which the system according to the invention canbe deposited are various: the layers can be deposited directly on theOLED support facing the active element thereof, but also on othersubstrates, such as monoadhesive or biadhesive sheets.

[0030] Mono- and biadhesive sheets are well known and widely used in anumber of technological applications. These sheets or tapes aregenerally formed of a support (a thin sheet of plastic material) on oneor both faces of which there is provided a layer of adhesive material.For example, the support can be made in polyethyleneterephtalate (PET),with thickness values within 4 and 20 micron (μm), whereas the adhesivelayers are made with acrylic materials having thickness values of theorder of the tens of micron. Said adhesive sheets are sold bymanufacturers with sheets of paper having the function of protecting theadhesive from contamination by external agents. Adhesive sheets or tapesof this kind are commercially available for example by Japanese companyNitto-Denko, with catalogue number HJ-3160W, or from Japanese companyTeraoka with catalogue number 707.

[0031]FIG. 1 shows the cross-section of an OLED device 10: on a firsttransparent planar support 101 is present the active element of thedevice formed of a first series 102 of transparent, linear and mutuallyparallel electrodes, a double layer of electroluminescent organicmaterials 103 conductors of electronic vacancies (holes) and ofelectrons, and a second series 104 of linear electrodes, mutuallyparallel and orthogonal to those of the first series. A second support105 planar and parallel to the first support is fixed thereto by meansof a glue, thus defining the internal space 106.

[0032]FIG. 2 shows the support 105 of OLED 10, on which is arranged thesystem according to the invention in a first embodiment thereof. Thesystem is formed of a layer 201 of material capable of sorbing hydrogen,directly deposited on the surface of the second support of the OLED andof a second layer 202 of a material capable of converting water intohydrogen, deposited onto the first layer.

[0033] Then, other embodiments are possible, which allow to obtain thesystem of the invention independently of the final device, that is,without involving elements of the latter during the preparation of saidsystem.

[0034] With this regard, the second embodiment of the invention is to beconsidered, shown in FIG. 3, which uses as a substrate a monoadhesivesheet: therein, the layer 304 of hydrogen sorbing material and the layer305 of material capable of converting water into hydrogen have beendeposited on a monoadhesive sheet 301, formed of a support 302, anadhesive layer 303. Soon after production, the system represented inFIG. 3 also comprises a protective sheet of paper covering the adhesivelayer, but this protective sheet is removed before placing the system incontact with support 105, and is thus not shown in the drawing.

[0035] The third embodiment of the invention is shown in FIG. 4;therein, the layer 405 of hydrogen sorbing material and the layer 406 ofmaterial capable of converting water into hydrogen are deposited on abiadhesive layer 401, formed of a support 402 covered on both sides withadhesive layers 403, 404 and with paper sheets of which only some partsare shown in the figure.

[0036] An alternate use of the invention relates to manufacturingprocesses of the system in some possible above described embodiments.

[0037] The layer of hydrogen sorbing material can be deposited by meansof a suitable technique which allows to form thin films: in the case oftitanium and of the unsaturated organic compounds of low molecularweight, evaporation can be used, while in the case of the zirconium andof the alloys in general it is necessary to use other techniques, suchas Physical Vapor Deposition, also known as PVD or “sputtering”, whichis well known in the art and does not need to be described here.

[0038] The film of material capable of converting water into hydrogen isdeposited on this first layer: to this purpose various evaporationtechniques can be used, among which, in the specific case of the barium,the technique based on the use of dispensers formed of threads having aU-shaped cross-section, which are loaded along the whole length thereofwith an alloy of the metal.

[0039] These threads are connected to an electric current generator andwhen this is activated, the threads are heated by Joule effect thusreaching a temperature at which it is observed the formation of vaporsof barium, which is allowed to deposit onto the layer of hydrogensorbing material.

[0040]FIG. 5 shows the process for obtaining the first embodiment shownin FIG. 2. Onto the OLED support 105 is positioned a first maskingelement 501 having an opening 502 (FIG. 5a). Since said openings arecalled in the field “ports”, said term will be used in the following. Onelement 501 is deposited, by means of one of the above mentionedtechniques, layer 201 of hydrogen sorbing material (FIG. 5b).Subsequently, said masking element is removed and substituted with asecond masking element 503 having a port 504 suitable for encompassinglayer 201 (FIG. 5c). The material capable of converting water intohydrogen is then deposited on said second masking element, thus forminglayer 202 (FIG. 5d). Finally, the second masking element is removed,leaving system 50 (FIG. 5e). In case it is desired to obtainsuperimposed layers having the same shape and size, it is not necessaryto use a second masking step, but it is possible to use a single maskingelement, having the desired shape and size.

[0041] Because of the very high reactivity of the water convertingmaterial it is essential that the system does not contact moisture ofthe air; for this reason it must be protected both during the productionand subsequently, maintaining it in an inert environment.

[0042]FIG. 6 schematically shows the process for obtaining the secondembodiment illustrated in FIG. 3: on the monoadhesive sheet 301 ispositioned a masking element 601, provided with a port 602 on thesurface thereof (FIG. 6a). Subsequently layer 304 of hydrogen sorbingmaterial is deposited (FIG. 6b). The used masking element is thenremoved and replaced with a second masking element 603 having a port 604suitable for encompassing completely layer 304 (FIG. 6c). Subsequentlyit is carried out the second deposition, by evaporation, of the materialcapable of converting water into hydrogen, thus forming layer 305 (FIG.6d). The next operation consists in removing said second masking elementand cutting the monoadhesive sheet around the perimeter of the systemthus obtaining th final system 60 (FIG. 6e).

[0043] Finally, in FIG. 7 and 8 there are schematically shown twopossible manufacturing processes of the third embodiment of theinvention by using a biadhesive sheet as a substrate; in this case, itis possible to deposit the layer of moisture sorbing material through astep of filling to the top level, by using one of the two layers ofadhesive.

[0044] The process schematized in FIG. 7 consists in providing abiadhesive sheet 401 and in incising one of the layers of paper 701which cover it, so as to selectively remove a portion 702 thereof and toleave uncovered the underlying adhesive 404: in this way a “cavity” 703with vertical walls having a height equal to the thickness of the sheetof paper is obtained, and with the bottom covered with adhesive (FIG.7a). The same paper thus works as a masking element for the nextoperation: said cavity is in fact filled to the top with the hydrogensorbing material 405 (FIG. 7b). Then, a masking element 704 having aport 705 such as to encompass the cavity filled to the top issuperimposed to the biadhesive (FIG. 7c) and the deposition of thematerial capable of converting water into hydrogen is carried out, whichtakes place on the masking element and on the cavity filled to the topwith the hydrogen sorbing material, thus forming a layer 406 (FIG. 7d).By removing said masking element it is obtained, in correspondence ofthe original cavity, system 70 according to the invention, which can beisolated by cutting the biadhesive sheet around the perimeter of saidsystem (FIG. 7e).

[0045] The process of FIG. 8 involves the following steps: first, one ofthe paper layers 701 of the biadhesive sheet 401 is incised thusallowing the removal of one portion 801 and the formation of the cavity802 (FIG. 8a). Subsequently, the same paper layer is incised again alongthe perimeter of a zone encompassing cavity 802 (FIG. 8b), thus defininga portion 803 of paper. Then, said cavity is filled to the top with thehydrogen sorbing material thus forming layer 405 (FIG. 8c); at thispoint portion 803 is removed, leaving an opening 804 such as toencompass layer 405 of hydrogen sorbing material (FIG. 8d). A maskingelement 805 having a port coincident with said opening is laid onto thebiadhesive (FIG. 8e) and the material capable of converting water intohydrogen is evaporated thereon thus forming layer 406 (FIG. 8f). Themasking is then removed and the biadhesive can be cut around theperimeter of the double layer leaving system 80 (FIG. 8g).

[0046] The processes described in the case that mono- or biadhesivesheet are used have been illustrated with reference to the production ofa single system, but, for reasons of productivity and economicity, theycan be realized continuously in a quick and reproducible way. As amatter of fact, in the first case continuously fed monoadhesive tapescan be used, whereon a double masking is conducted in order to depositselectively, by means of evaporation, the moisture sorbing material andthe barium layer so as to form at the same time a number of systems.Subsequently the single systems can be obtained by shearing ormechanical cut, or alternatively, it is possible to carry out a punchingstep, by cutting with suitable tools the monoadhesive sheet along theedges of the different systems, but leaving the protective paperintegral. Continuous tapes can be obtained in this way, on which anumber of systems according to the invention are provided, which canthen be separated from time to time like adhesive labels.

[0047] The same result is obtained by carrying out the punching step onthe monoadhesive sheet before the deposition of the system according tothe invention. Two different processes can be carried out in the case ofthe biadhesive sheet, as already observed. In the first case the stepsto be carried out are the following: first, incision of one of the paperlayers is carried out, defining the portions whereon the systemsaccording to the invention will be formed, and the parts of paper oversaid portions are removed, thus obtaining cavities with vertical wallshaving a height equal to the thickness of the paper sheet, and with thebottom covered by adhesive. Then, filling to the top of said cavitieswith the hydrogen sorbing material is carried out. Subsequently, asecond masking is realized with a masking element having ports such asto encompass the cavities filled to the top and evaporation of thematerial capable of converting water into hydrogen is carried out; whensaid evaporation is completed, the masking element is removed and thestep of cutting or punching is at last carried out. In the last case,one obtains continuous tapes whereon a number of systems according tothe invention are present, which can then be separated from time to timeand applied to the supports of the final devices.

[0048] On the contrary, in order to carry out the second process thesteps to be carried out are: first incision on one of the paper layersin order to define the portions on which the systems according to theinvention will be formed, removal of the paper parts on said portionswith formation of cavities, second incision along the perimeter of zonessuitable for encompassing said cavities. The subsequent steps consist infilling to the top level the cavities with the material capable ofsorbing hydrogen thus forming the correspondent layers, in removing thepaper covering said zones encompassing the original cavities, in maskingand depositing the second layer of material capable of converting waterinto hydrogen. After the removal of said masking the single systems canbe then obtained also in this case by shearing or mechanical cut orpunching.

[0049] As already observed in the case of the monoadhesive sheet, thestep of punching the biadhesive sheet can also be carried out before thedeposition of the system according to the invention.

Having thus described our invention, we claim:
 1. A system for theremoval of water and hydrogen comprising: two superimposed layersdirectly in contact with each other, a first layer which is formed of amaterial capable of sorbing hydrogen, a second layer formed of amaterial capable of converting water into hydrogen.
 2. The system asrecited in claim 1 wherein said material capable of converting waterinto hydrogen is selected among alkali or alkali-earth metals.
 3. Thesystem as recited in claim 2 wherein said material is barium.
 4. Thesystem as recited in claim 1 wherein said hydrogen sorbing material isselected among from the group consisting of systems comprisingunsaturated compounds and hydrogenation catalysts, titanium, zirconium,titanium-zirconium alloys, titanium alloys having a titanium weightpercent not lower than 50%, zirconium alloys having a zirconium weightpercent not lower than 50%.
 5. An electronic device containing a systemfor the combined removal of water and hydrogen, said system comprisingtwo superimposed layers directly in contact with each other, said firstlayer of which is formed of a material capable of sorbing hydrogen, saidsecond layer formed of a material capable of converting water intohydrogen, whereby said device is water sensible.
 6. The device asrecited in claim 5, consisting in a screen of the type withlight-emitting organic diodes, formed of a first transparent support andof a second support joined along the whole perimeter thereof with asealing material wherein an internal space is created; further comprisedof a structure in contact with the first support formed of two series ofelectrodes orthogonal to each other with interposed a double layer ofelectroluminescent organic materials.
 7. The screen according to claim6, wherein the layer formed of a material capable of converting waterinto hydrogen faces the internal space.
 8. A process for manufacturing asystem two superimposed layers directly contacting each other, saidfirst layer which is formed of material capable of sorbing hydrogen,said second layer formed of a material capable of converting water intohydrogen, comprising the steps of: preparing a substrate; depositing onsaid substrate a first layer of a material selected between hydrogensorbing material and material capable of converting water into hydrogen,having also arranged on said substrate a masking element; depositing asecond layer of a material selected between hydrogen sorbing materialand material capable of converting water into hydrogen wherein saidsecond layer has a different function from said material of the firstlayer.
 9. The process according to claim 8 wherein said material of saidfirst layer is the hydrogen sorbing material.
 10. The process accordingto claim 8 wherein said same masking element used in said deposition ofsaid first layer is used in said step of depositing the second layer ofmaterial.
 11. The process according to claim 8 wherein a second maskingelement having different ports from those of said masking element usedin said deposition of said first layer, is used in said step ofdepositing said second layer of material
 12. The process according toclaim 11 wherein said second masking element has ports of larger sizethan said masking element used for said deposition of said first layer,such that said second layer covers completely said first layer.
 13. Theprocess according to claim 8 wherein said substrate is one of the twosupports of a screen of the type with light-emitting organic diodes. 14.The process according to claim 8 wherein said substrate is amonoadhesive sheet.
 15. The process according to claim 14 furthercomprising a step of punching said monoadhesive sheet after the systemaccording to claim 1 has been deposited on said monoadhesive sheet. 16.The process according to claim 14 further comprising a step of punchingsaid monoadhesive sheet before the system according to claim 1 isdeposited on said monoadhesive sheet.
 17. The process according to claim8 wherein said substrate is a biadhesive sheet.
 18. The processaccording to claim 17, further comprising the steps of: providing abiadhesive sheet comprising two sheets of protective paper; incising onesheet of protective paper along the edges of some portions thereof;removing said portions thus forming cavities; filling to the top levelsaid cavities with a first layer of a material; arranging a maskingelement on said biadhesive sheet, wherein said masking element havingports encompassing said cavities filled to the top level; depositing asecond layer of a material; and removing said masking element.
 19. Theprocess according to claim 18, further comprising a step of punchingsaid biadhesive sheet while leaving integral said layer of protectivepaper opposed to that on which said system has been deposited, saidpunching made before the deposit of said first layer of material orafter removal of said masking element.
 20. The process according toclaim 17 further comprising the steps of: providing a biadhesive sheetcomprising two sheets of protective paper; incising one sheet ofprotective paper along the edges of some portions thereof; removing saidportions thus forming cavities; incising said sheet of protective paperalong the perimeter of portions encompassing said cavities; filling tothe top level said cavities with a first layer of a first material;removing said paper covering said zones, so as to form openingsencompassing said first layer of material; arranging a second maskingelement on said biadhesive sheet, said masking element having portscoinciding with said openings; depositing a second layer of a secondmaterial; and removing said masking element.
 21. The process accordingto claim 20, further comprising a step of punching said biadhesive sheetwhile leaving integral said layer of protective paper opposed to thatwhere said system is deposited, said punching step being carried outbefore said deposition of said first layer of material or after saidremoval of said masking element.